Helicopter's of the type having turbine engines typically include turbine outlet temperature monitors to avoid “hot starts.” For example, it is well known that during the first few seconds of an engine start up procedure, the turbine outlet temperature will accelerate at a rapid rate. It is also well known to abort a start if either a maximum temperature, as for example 927° C. or an 810° C. to 927° C. maximum ten second transition limitation is about to be exceeded. It is also well known to operate helicopter engines below predetermined levels of turbine output temperature, torque and engine speed which are referred to herein as over-stress limits. Failure to operate within such limits may seriously damage an engine and/or lead to an engine failure.
One approach for starting a gas turbine of the type used for generating electric power is disclosed in the U.S. Pat. No. 5,121,596 of Takehara et al. As disclosed therein, a gas turbine is started while injecting a prescribed amount of moisture into a path for combustion gas from the start up of the gas turbine and the amount of moisture is varied dependent upon the feed quantity of fuel or the temperature of the combustion gas. In this way, the combustion temperature in the combustor or temperature variation rate on the surfaces of component parts in a gas path are approximately equal.
An additional U.S. Pat. No. 4,619,110 of Moore discloses a helicopter engine warning or control system which includes arrangements for sensing the engine temperature, the engine speed and the output torque from the engine. An audible warning is provided which may vary as the over-stress limits are approached. In addition, an arrangement may be provided for automatically injecting water or alcohol into the engine as an over-stress condition is approached.
It is now believed that there may be a commercial demand and need for an improved helicopter turbine engine protection system in accordance with the present invention. There should be a commercial demand and need for such methods and systems which are used during start up of a helicopter turbine engine to avoid “hot starts.” In some cases the system will avoid the need to abort the start.
In addition, the improved systems in accordance with the present invention are also effective in avoiding an over-stress situation during flight operations.